function ab = quaternProd(a, b)
%QUATERNPROD Calculates the quaternion product
%
%   ab = quaternProd(a, b)
%
%   Calculates the quaternion product of quaternion a and b.
%
%   For more information see:
%   http://www.x-io.co.uk/node/8#quaternions
%
%	Date          Author          Notes
%	27/09/2011    SOH Madgwick    Initial release

    ab(1) = a(1).*b(1)-a(2).*b(2)-a(3).*b(3)-a(4).*b(4);
    ab(2) = a(1).*b(2)+a(2).*b(1)+a(3).*b(4)-a(4).*b(3);
    ab(3) = a(1).*b(3)-a(2).*b(4)+a(3).*b(1)+a(4).*b(2);
    ab(4) = a(1).*b(4)+a(2).*b(3)-a(3).*b(2)+a(4).*b(1);
end

